This invention relates to telecommunication systems that support both plain old telephone services (POTS) and digital subscriber line services (XDSL). The invention is especially suited but not limited to allocating overhead voltage for both the POTS and XDSL signals.
In the United States, telephone networks use batteries of approximately 48 to 52 Volts (V) of direct current (DC), located at a central office, to drive customer premises equipment (CPE), such as a standard telephone, at a customer premises. In a POTS mode of operation, a normal office battery voltage is acceptable because a standard CPE device typically needs at least between 16 to 22 milliamps (mA) of DC current to operate. The impedance of the telephone loop (path between the central office and the CPE) typically changes based on the loop configurations. When POTS and XDSL are transmitted simultaneously, the combination of POTS and XDSL overhead voltages along with the needed DC voltage are not fully supported by the output of the battery on some loop configurations. This results in lowering the maximum data rates of the XDSL signal and/or the voice quality of the POTS signal.
Attempts at solving this problem have included using higher voltage batteries, separate drive circuits for POTS and XDSL, and battery boost circuits. However, each of these solutions have included expensive new circuitry and the associated software to control it. Therefore, there is a need for a system and method for allocating overhead voltage to allow the transmission of POTS and XDSL signals either separately or simultaneously. There is a need to permit the use of normal office batteries in the United States with standard central office batteries.
The above problems are solved and a number of technical advances are achieved in the art by implementation of a system and method that allows allocation of overhead voltage in the transmission of POTS and XDSL signals. In accordance with the invention, a method for allocating overhead voltage in a communication system for transmission of POTS and XDSL signals is described. The method comprises the steps of determining a communication state of a call for the communication system and allocating the overhead voltage in response to the communication state of the call.
Also, in accordance with the invention, a communication system for allocating overhead voltage between a telephonic equipment devicexe2x80x94such as a switch, digital loop carrier (DLC), or digital subscriber line access multiplexer (DSLAM)xe2x80x94and a user device is described. The system comprises a line driver, located in the telephonic equipment device (telephonic switch), in signal communication with the user device wherein the line driver is in one of a plurality of communication states. The system also includes a processor in signal communication with the line driver, wherein the processor allocates the overhead voltage in response to the communication state of the system.
The foregoing advantageous features of the invention will be described in detail and other advantageous features will be made apparent upon reading the following detailed description that is given with reference to the several figures of the drawings in which:
FIG. 1 is a functional block diagram of a communication system of the present invention;
FIG. 2 is a functional block diagram of the line driver of FIG. 1;
FIG. 3 illustrates the setting of overhead voltages, by the processor of FIG. 1, to allow for the passage of POTS or XDSL signals; and
FIG. 4 is a logical flow diagram showing the steps performed by the communication system shown in FIG. 1.